This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-114126, filed Apr. 14, 2000; and No. 2001-006859, filed Jan. 15, 2001, the entire contents of both of which are incorporated herein by reference.
The present invention relates to a method and equipment for assessing the duration of life of members put under a high in-service temperature environment for a long period and more specifically to a method and equipment for assessing the duration of life of each member put under a high in-service temperature environment for a long period, for example, the high or intermediate pressure rotor, the high or intermediate pressure casing, and the main stop valve, that are incorporated into a steam turbine unit.
Conventionally, a member which is put under a high in-service temperature environment for a long period, for example, the rotor in a steam turbine unit, is subjected continuously to a load for a long period in a high in-service temperature environment and hence suffers creep damage; as a consequence, its duration of life is reduced. Also, the rotor is repeatedly subjected to thermal stresses at the times of starting and stopping the turbine, resulting in the reduced duration of life. To ensure the reliability of the steam turbine unit over a long period, therefore, it is important to assess the duration of life of its structural members with precision.
Heretofore, as a technique to assess the life of such members, one has been developed and put to practical use which involves subjecting virgin materials for new components and used materials of components which have been put at high in-service temperatures and are to be scrapped at the time of replacement to a destructive test and assessing their residual life on the basis of the material characteristic test results. That is, in the destructive test, the creep rupture strength and the low-cycle fatigue strength of those materials are obtained on a laboratory basis. The creep rupture strength and the low-cycle fatigue strength are obtained as a function of a certain parameter, for example, a function of hardness. In inspecting a steam turbine unit regularly, the hardness of the individual members is measured as their intrinsic parameter. From the intrinsic parameters of the individual members, i.e., the creep rupture strength and low-cycle fatigue strength data as a function of hardness, the operation history of the unit and its residual life allowing for future operation are assessed.
An example of a technique to assess the residual life is one disclosed in Jpn. Pat. Appln. KOKAI No. 1-27378. The technique of residual life assessment disclosed in this publication involves calculating the temperature-stress characteristic of a structural member subjected to a high in-service temperature from its working condition value, calculating the material characteristic of the structural member from its hardness, calculating the damage cumulative value of the structural member by adding corrections corresponding to the operation history to these characteristics by condition setup equipment, and comparing the damage cumulative value with an allowable value. It is said that such a technique can predict accurately the time when a crack is initiated in the structural member.
Conventionally, the life of individual members is obtained for each unit. In this life assessment, the creep damage and the thermal fatigue damage or low-cycle fatigue damage are obtained by linear cumulative damage rules and a method to assess the residual life allowing for future operation is adopted. Thus, the conventional methods, which assess the residual life for each unit or for each member in each unit, can produce variations in assessment and cannot make assessment quickly. From this point of view, the development of a technique to assess the residual life of structural members precisely and quickly has been demanded in recent years.
Conventionally, in assessing the life of a member in a turbine or the like, its hardness is measured at regular inspection (in-service inspection) time and the life is assessed utilizing the measured hardness. Unless the hardness is measured at regular inspection time, life assessment cannot be made with precision. It is difficult to measure the hardness at any desired time.
To ensure precise and quick life assessment, a method is required which collects changes with time in the hardness of each individual member and stochastically estimates the hardness of a member in a turbine or the like to thereby assess its life.
It is an object of the present invention to provide a method and equipment which permit the life of a structural member put under a high in-service temperature environment to be assessed precisely and quickly.
It is another object of the present invention to provide a method and equipment which, by collecting changes with time in the hardness of each individual member put under a high in-service temperature environment, permits its hardness to be estimated stochastically and its life to be assessed precisely and quickly.
According to an aspect of the present invention, there is provided a method of assessing the life of a member subjected to a high in-service temperature for a long period comprising the steps of:
determining a Larson-Miller parameter for the member whose life is to be assessed from the in-service temperature and a service time period during which the member is used in-service temperature, and calculating the creep damage degree on the basis of cumulative damage rules from the hardness and stress of the member to establish data; and
approximating the relationship between the Larson-Miller parameter and the creep damage degree by an expression including an exponential function.
According to an aspect of the present invention there is also provided a method of assessing the life of a member subjected to a high in-service temperature for a long period comprising the steps of:
determining a Larson-Miller parameter for the member whose life is to be assessed from the in-service temperature and service time period during which the member is used in-service temperature and using data established by calculating the creep damage degree on the basis of cumulative damage rules from the hardness and stress of the member to approximate the relationship between the Larson-Miller parameter and the creep damage degree by an expression including an exponential function; and
estimating the creep damage degree by adding probabilistic statistical processing to the approximate expression.
Furthermore, according to an aspect of the present invention there is provided a method of assessing the life of a member provided in an apparatus which is started and stopped over and over again and subjected to a high in-service temperature for a long period while the apparatus is being operated comprising the steps of:
calculating an estimation parameter which is a function of a set of the start count and thermal stress, and thermal fatigue and damage degree based on cumulative damage rules for the member whose life is to be assessed and establishing data; and
approximating the relationship between the estimation parameter and the thermal fatigue and damage degree by an approximate expression.
According to an another aspect of the present invention, there is also provided an apparatus for assessing the life of a member subjected to a high in-service temperature for a long period, comprising:
means for determining a Larson-Miller parameter for the member whose life is to be assessed from the in-service temperature and a service time period during which the member is used in-service temperature, and calculating the creep damage degree on the basis of cumulative damage rules from the hardness and stress of the member to establish data; and
means for approximating the relationship between the Larson-Miller parameter and the creep damage degree by an expression including an exponential function.
According to an yet another aspect of the present invention, there is also provided an n apparatus for assessing the life of a member subjected to a high in-service temperature for a long period comprising:
means for determining a Larson-Miller parameter for the member whose life is to be assessed from the in-service temperature and service time period during which the member is used in-service temperature and using data established by calculating the creep damage degree on the basis of cumulative damage rules from the hardness and stress of the member to approximate the relationship between the Larson-Miller parameter and the creep damage degree by an expression including an exponential function; and
means for estimating the creep damage degree by adding probabilistic statistical processing to the approximate expression.
Furthermore, according to a yet another aspect of the present invention, there is provided an apparatus for assessing the life of a member provided in an apparatus which is started and stopped over and over again and subjected to a high in-service temperature for a long period while the apparatus is being operated comprising:
means for calculating an estimation parameter which is a function of a set of the start count and thermal stress, and thermal fatigue and damage degree based on cumulative damage rules for the member whose life is to be assessed and establishing data; and
means for approximating the relationship between the estimation parameter and the thermal fatigue and damage degree by an approximate expression.
Furthermore, according to a yet further aspect of the present invention, there is also provided an apparatus for assessing the life of a member provided in an apparatus which is started and stopped over and over again and subjected to a high in-service temperature for a long period while the apparatus is being operated comprising:
means for using an estimation parameter which is a function of the start count and thermal stress, and data established by calculating thermal fatigue and damage degree based on cumulative damage rules, for the member whose life is to be assessed, and approximating the relationship between the estimation parameter and the thermal fatigue and damage degree by an approximate expression; and
means for estimating the thermal fatigue and damage degree by adding probabilistic statistical processing to this approximate expression.
Furthermore, according to a yet another aspect of the present invention, there is provided a method of assessing the life of a member subjected to a high in-service temperature for a long period comprising the steps of:
determining a Larson-Miller parameter for the member whose life is to be assessed from the in-service temperature and time of the member and using data established by calculating the creep damage degree on the basis of cumulative damage rules from the hardness and stress of the member to approximate the relationship between the Larson-Miller parameter and the creep damage degree by an expression including an exponential function;
prompting a terminal connected through a network to input the in-service time period, of the member whose life is to be assessed;
assessing the life of the member from the in-service time period, of the member whose life is to be assessed by using the approximate expression; and
outputting the assessed life to the terminal.
According to a yet further aspect of the present invention, there is provided an apparatus for assessing the life of a member subjected to a high in-service temperature for a long period comprising:
means for determining a Larson-Miller parameter for the member whose life is to be assessed from the in-service temperature and time of the member and using data established by calculating the creep damage degree on the basis of cumulative damage rules from the hardness and stress of the member to approximate the relationship between the Larson-Miller parameter and the creep damage degree by an expression including an exponential function;
means for prompting a terminal connected through a network to input the in-service time period, of the member whose life is to be assessed;
means for assessing the life of the member from the in-service time period, of the member whose life is to be assessed by using the approximate expression; and
means for outputting the assessed life to the terminal.
According to a yet further aspect of the invention, there is provided an apparatus for assessing the life of a member subjected to a high in-service temperature for a long period comprising:
means for determining a Larson-Miller parameter for the member whose life is to be assessed from the in-service temperature and service time period during which the member is used in-service temperature and using data established by calculating the creep damage degree on the basis of cumulative damage rules from the hardness and stress of the member to approximate the relationship between the Larson-Miller parameter and the creep damage degree by an expression including an exponential function and further to prepare an expression estimating the creep damage degree added with probabilistic statistical processing;
means for prompting a terminal connected through a network to input the in-service time period, and the hardness of the member whose life is to be assessed;
means for assessing the life of the member from the in-service time period, of the input member; and
means for outputting the assessed life to the terminal.
In the above described method and apparatus, the Larson-Miller parameter P is calculated by an expression given as
P=(T+273)(log t+C)
where C is the material constant, T is the in-service temperature and t is the in-service time period, and the creep damage degree xcfx86c based upon the cumulative damage rules is calculated by an expression given as
Pxe2x80x2=A1("sgr")H+B1("sgr")
where "sgr" is the stress, and H is the hardness,
Pxe2x80x2=(T+273)(log tr+C)
where C is the material constant, T is the in-service temperature, and tr is creep rupture life,
xcfx86c=t/(tr+t) or xcfx86c=t/tr
where xcfx86c is the creep damage degree, and
where, when data of the hardness of the portion under a high in-service temperature and a high stress of the member whose life is to be assessed is used, xcfx86c=t/(tr+t) is employed, and when data of the hardness of the portion under a high in-service temperature and a low stress is used to assess the portion of the member under a high in-service temperature and a high stress, xcfx86c=t/tr is employed.
In the above described method and apparatus, the creep damage degree xcfx86c is obtained by
xcfx86c=1xe2x88x92exp(Axc2x7PB)
wherein A and B are constants and P is the Larson-Miller parameter.
In the above described method and apparatus, the creep damage degree where the probabilistic statistical processing is added to the approximate expression is also estimated by an expression given as
xcfx86c={1xe2x88x92exp(Axc2x7PB)}xc2x7{xcex2xc2x7m{square root over (ln(1xe2x88x92Pf)xe2x88x921)}}
where m is the Weibull coefficient, xcex2 is the scale parameter, and Pf is the cumulative probability.
the cumulative probability Pf corresponds to the cumulative probability Pf defined by the following expression and the cumulative probability Pf depending on the hardness is obtained by an expression given as
Pf=1xe2x88x92exp{xe2x88x92(xcexc/xcex2)m}
where m is the Weibull coefficient, xcex2 is the scale parameter, and xcexc is the hardness of the member (experimental value)/the hardness of the member (estimated value), and
further the estimated value of the hardness of the member is obtained by an equation using the least squares method given as
at+b,
where t is the total operation time when the hardness of the member is measured, and a and b are constants.
In the above described method and apparatus, the hardness of the member is estimated by a probabilistic expression given as
H=(at+b)(xcex2xc2x7m{square root over (ln(1xe2x88x92Pf)xe2x88x921)}) 
wherein H is the hardness of the member, t is the total operation time when the hardness of the member is measured, a and b are constants, m is the Weibull coefficient, xcex2 is the scale parameter, and Pf is the cumulative probability corresponding to the hardness of the member.
In the above described method and apparatus, the estimation parameter q is given by an expression of
xe2x80x83q=N("sgr"cxc2x7nc/N+"sgr"wxc2x7nw/N+"sgr"hxc2x7nh/N)xcex1
where xcex1 is the constant, "sgr"c is the thermal stress of the member at cold start time, "sgr"w is the thermal stress of the member at warm start time, "sgr"h is the thermal stress of the member at hot start time, N is the total start count, nc is the cold start count, nw is the warm start count, and nh is the hot start count, and the thermal fatigue and damage degree is approximated by an expression given as
xcfx86f=Cxc2x7q
where Cf is a constant.
In the above described method and apparatus, the thermal fatigue and damage degree obtained by adding the probabilistic statistical processing to the approximate expression is given by an expression of
xcfx86f=Cfxc2x7q(xcex2xc2x7m{square root over (ln(1xe2x88x92Pf)xe2x88x921)})
where m is the Weibull coefficient, xcex2 is the scale parameter, and Pf is the cumulative probability.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.